The disclosure relates to key locked inserts. More particularly, the disclosure relates to tools for installing key locked inserts.
Key locked inserts are commonly used broadly in industry to provide a replaceable threaded attachment point (typically to a metal workpiece). A particular situation is in gas turbine engines (broadly including turbofans, turbojets, turboprops, turboshafts, and industrial gas turbines), typically to attach external components to case pieces of the engine (e.g., pipe hangers, accessories, and the like).
A key locked insert (insert) 20 (FIG. 6) comprises a bushing or body 22 extending along a central longitudinal axis 500 from a first end or rim 24 to a second end or rim 26. The body 22 has an inner diameter (ID) thread (internal thread) 28 along a central passageway 30 and an outer diameter (OD) thread 32 along a periphery. Keys (wedges) 34 are fitted in respective axial grooves or slots 36 cut into the OD thread 32. Typically, smaller diameter or lighter duty inserts have two diametrically opposed keys while larger or heavier duty inserts have four evenly spaced keys. The keys 34 each extend from a proximal (viewed relative to the body) end 38 to a distal end 40. The keys 34 each have a radially protuberant portion 44 near the distal end 40 and a radially narrower portion 42 near the proximal end 38. Prior to use, the keys 34 are in an extended condition (FIG. 6) with the protuberant portion 44 protruding beyond the second end 26.
In use, a user threads the insert body 22 into a complementary internally-threaded hole 50 (FIG. 7) in a workpiece 52 (e.g., a metal workpiece such as a gas turbine engine case segment) via the OD thread 32. The threading may place the second end 26 flush or slightly sub-flush to the adjacent face 60 of the workpiece. The user then drives the keys 34 axially through the workpiece's ID thread 54 (FIG. 8—with the protuberant portions 44 creating broached slots 56). The interfitting of the keys 34 with the slots 36 and 56 serves as an anti-rotation feature for the body 22.
In engine service, the internal thread 28 of the insert 20 may be damaged. Sometimes, the insert 20 may be replaced. For example, the insert 20 may be removed by first drilling the insert 20 with a drill of slightly smaller diameter than the troughs of the insert's OD thread 32 and just far enough axially to sufficiently weaken the body 22 material adjacent to the protuberant portions 44 of the keys 34. Then, the user knocks the keys 34 out of the slots broached 56 (e.g., radially inward with a punch and hammer) and unscrews the insert body 22 from the workpiece 52 (e.g., using a screw extractor tool).
A new insert 20 may be installed either using the broached slots 56 from the prior insert (if they are in good condition) or creating new broached slots angularly offset from the prior ones by an angle θ (FIG. 9; the clocking position or angle—see discussion below). The number of times an insert 20 can be replaced is limited to the number and condition of existing broach slots 56 and the specified θ. FIGS. 9 and 10 show the keys 34 before driving.
Alternatively to reusing the prior threaded hole 50 in the workpiece, the hole can be bored out to then next incremental available diameter and tap threaded. A new insert may be installed that has an OD thread 32 complementary to the ID thread 54 of the newly bored and threaded hole but having the same ID thread as the prior insert. This may be a necessity when there is no remaining available space for new broached slots 56.
To aid in insert installation, two general types of installation tools exist: manual and pneumatic. U.S. Pat. No. 6,704,985, to Marshall, Mar. 16, 2004, and entitled “Threaded tool insert”, discloses a manual tool. U.S. Pat. No. 4,752,996, to Berecz et al., Jun. 28, 1988, and entitled “Insert installation tool”, discloses a pneumatic tool.
In exemplary manual tools, the keys 34 are driven via hammer striking force on the distal ends 40 (e.g., with the tool intervening between the hammer and the keys). Prior to said driving, the user may rotate the insert 20 to the desired orientation. The desired orientation may be at existing, serviceable, broached slots 56 or at a predetermined angle θ (in both directions) from unserviceable broached slots (e.g., a repair specification may specify an angle that has been calculated based on workpiece material, insert diameter, broached slot width, and the like). Manual tools risk deforming or breaking keys due to factors such as variations in hammer striking force magnitude and direction and improper support for the workpiece, causing key deflection and improper installation. This risk increases with the material hardness of the workpiece.
Exemplary pneumatic tools have a mandrel that threads into an uninstalled insert. The tool then automatically threads the insert into the workpiece and immediately thereafter drives the keys by pneumatic actuation. One advantage of this is the tool's exerted forces are well aligned and counteracted because the tool is threaded into the insert and thus the workpiece. A disadvantage is the angular position of the keys about the hole axis cannot be controlled. As a practical matter, this limits use of the pneumatic tool to situations where no broach slots are present (e.g., at original equipment manufacture (OEM) or for a newly oversized hole).